The Israeli navy has refused to allow an Iranian aid ship deliver medicine, food and clothing to the Gaza Strip.
The humanitarian group sponsoring the vessel said Israeli warships approached it 20 miles off the Gaza coast today and ordered it to turn back.
The ship is carrying 2,000 tons of aid for Palestinians suffered as a result of Israel's 18-day bombardment of Gaza.
Iran has already announced sanctions on foreign companies with Israeli links as a result of the military onslaught, which has killed almost 1,000 Palestinians.
It has also encouraged Muslims across the world to boycott all products that Israelis may profit from.